Non-linear resistance device



Nov. 6, 1956 1. A. LESK 2,769,926

NONLINEAR RESISTANCE DEVICE Filed March 9, 1953 3 Sheets-Sheet 1 Fig?)IsraelALesk,

dwrfim His Attorney Nov. 6, 1956 A. LESK NON-LINEAR RESISTANCE DEVICE 3Sheets-Sheet 2 Filed March 9, 19543 Inventor l'r'ael A.Le sk by HisAttorney.

Nov. 6, 1956 I. A. LESK NON-LINEAR RESISTANCE DEVICE iled March 9, 19535 Sheets-Sheet 5 Inventor: lsraelAL'esk,

HisAttofney.

United States 2,7 69,926 N N JJN'EAK RESESTANCE DEVICE Application March9, 1%3, Serial No. 341,164 9 Claims. (Cl. 307-385) This inventionrelates to non-linear resistance devices and more particularly to suchdevices formed of semi-- conductive material and to circuit arrangementsutiliz ing such devices.

The theory of electric conduction in solids by means of holes andelectrons, as it is presently understood, is assumed to be well known tothose skilled in this art. Therefore, only a brief summary of so much ofthe theory as is thought necessary to understand the present inventionwill here :be presented.

As is well known, semiconductive materials are classitied as P-typesemiconductive materials and N type semi conductive materials. The typeof predominant activator material included in the semiconductivematerial determines the class into which the material falls.

jority activator in Isemiconductive materials, trons therefrom and thuscreate a deficiency of electrons in the vsemicond-uctive material. Thespaces left by the electrons trapped by the acceptor activator arecalled holes and act as though they were mobile positivelychargedelectrons. It can be said, therefiore, that in P-type semiconductivematerials, conduction takes place with holes as positively-chargedcurrent carriers.

Donor activator materials, when present as the ma- If the P-typematerial is maintained at a positive potential relative to the N-typematerial, the holes in the P-type material are repelled from thepositive potential and mi grate toward the N-type material under theinfluence of the electric field. The holes travel throughthe N-typeneutralized by excess electrons in the N-typ'e material. Similarly,excess electrons from the N-type region migrate across the P-N junctioninto the is called forward bias.

If, however, the P-type material is biased negatively with respect tothe N-type material, the holes in the P-type material and the excesselectrons in the N-type material are attracted away from the" junction;Thus the area in the vicinity of the P-N junction is almost devoid ofcarriers and little current fl'ows. The small resulting current iscaused by free holes and free electrons, created thermally, that migrateto the barrier region, travel across the junction, and combine with theexcess carriers in the opposite region. This small resulting current iscalled- 2,769,926 Fatented Nov. 6, 1956 either NP-N or P-N-P junctiontransistors depending on joined. Both types of junction transistorsexhibit similar properties and differ mainly in carrier types and inbias polarities required.

Conventional junction transistors, however, require two P-N junctions.Further, these junctions must be accurately positioned relatively toeach other and must be separated by only a very small distance foroptimum performance. As a result, junction transistors are very costly,ditficult to make, and further, require complex equipment in theirmanufacture.

Accordingly, it is an object of this invention to provide asemiconductor amplifying device utilizing only a single P-N junction.

Another object of this invention is to provide an improved semiconductordevice that exhibits negative resistance characteristics.

A further object of this invention is toprovide a semi conductor devicethat is useful as a switching relay whereby a small amount of energycontrols the flow of a large amount of energy.

The objects of my invention may be realized through the provision of aPN junction formed by a region of P-type semiconduc'tive materialcontiguous with a region of N-type semiconductive material, and meansfor biasing a portion of said junction in the forward directionand theremaining portion in the reverse direction.

The features of my invention which I believe to be novel are set forthwith particularity in the appended claims. My invention itself,

nection with the accompanying drawings wherein:

Pig. 1 is a plan view of a semiconductor device embodying the principlesof t 's invention with the biasing circuits therefor schematicallyshown;

Fig. 2 is a front view of the device illustrated in Fig. 1;

Figs. 3-5 are front views of the device illustrated in Fig. 1, and showthe charge distribution around the P-N junction for various relativevoltage magnitudes;

Figs. 6-8 are graphs of voltage plotted against distance for variousrelative magnitudes of voltages and correspond to the chargedistribution as shown in Figs. 35 respectively;

Fig. 9 is a graph of voltage versus current for the device shown in Fig.1;

Fig. 10 is a schematic circuit diagram of a relay utilizing. thesemiconductor device shown in Fig. 1, and

Fig. 11 is a schematic circuit diagram showing a modification of therelay illustrated in Fig. 10.

Referring to Fig. 1, a semiconductor device, designated comprises anelongated single crystal bar 12 of any suitab e N-typesemiconductivematerial such pellet 23 of an acceptor activator materialsuch as indium is located at the'approximate midpoint of one face of thebar 12.

During manufacture, the dot 23 is heated and a portion of the acceptoractivator material is fused into the bar 12. Although there are donoractivators present in the material, sufficient acceptor activator fusesinto the semiconductive material so that acceptor activators predominateand a region 25 (Fig. 2) below the dot 23 becomes a P-type semiconductorregion. Thus a rectifying P-N junction as indicated at 27 exists in thebar 12. The method of producing such a PN junction is not in itself apart of this invention. Suitable methods of, and apparatus for, theconstruction thereof are disclosed and claimed in a copendingapplication of William C. Dunlap, Jr., Serial No. 187,490, filedSeptember 29, 1950, now abandoned, and assigned to the assignee of thepresent application.

As shown in Fig. l, the bar 12 is composed of N-type semiconductivematerial and the dot 23 is composed of acceptor activator material. Thesame performance characteristics are obtained, however, if the dot 23 isdonor activator material and the bar 12 is P-type semiconductivematerial. The only change necessary is a reversal of the polarity of thebias voltage sources to be described.

A suitable source of direct voltage, here indicated by the battery 21,is connected to the conductors 17 and 19 to establish a unidirectionalpotential along the longitudinal axis of the bar 12. As shown in'Figs.6-8, a potential gradient exists in the bar 12, the potential having itsminimum value at one end of the bar 12 and its maximum value at theopposite end. Another source of bias voltage, here shown as a battery29, is connected between the dot 23 and the ohmic nonrectifying contact13 by conductors 31 and 33. The battery 29 can be connected betweeneither ohmic contact 17 or 19, all that is required is that terminal ofthe battery 29 that is connected to the contact 13 or 15 be of the samepolarity as the terminal of the battery 21 that is connected to the samecontact.

The range of values of the voltage of battery 29 is critical and itsmagnitude relative to the magnitude of the voltage of battery 21 isdeterminative of the negative resistance characteristics of the device11, as will appear.

The effects of various magnitudes of bias voltage on the device 11 canbest be understood by reference to Figs. 3-5 wherein the battery 29 isreplaced by a variable voltagesource such as a variable battery 35.

In the following discussion it is assumed that the side of the P-Njunction to which Va is connected, here shown as a dot 23, isequipotential. This is essentially true in practice since the dot 23 ismade of a good electrically conducting material.

In referring to Figs. 3-5, and in correlating them'to Figs. 6-8, theleft-hand end of the bar 12, which is connected to the negativeterminals of batteries 21 and 35, is considered as a reference point ofzero voltage.

Attention is first directed to the circuit illustrated by Fig. 3 whereinthe value of the voltage derived from battery 35 is adjusted to a valuemuch greater than one-half the magnitude of the voltage impressed bybattery 21 along the longitudinal axis of bar 12. For this relation ofvoltages, the P-type region 25 is positive relative to the N-type regionimmediately below the junction 27 because the voltage impressed inP-type region 25 from battery 35 is positive and is greater than thepositive voltage existing in the bar 12 at all points below the junction27 due to the battery 21. This is a forward bias for the junction 27 andthe area of the entire junction 27 consequently emits holes.

Fig. 6 shows a graph of the voltage along the longitudinal axis of thebar 12 plotted against the distance along the bar 12 as measured fromthe left end thereof. The non-linearity results from the flow of currentinto the bar 12 from the junction 27. As can be seen from Fig. 6, thevoltage applied to the dot 23, V0, is considerably greater than one-halfthe magnitude V0 of voltage applied to the length of bar 12.

In the circuit shown in Fig. 4, the value of the voltage 'c of battery35 is decreased to a magnitude considerably smaller than one-half themagnitude of the voltage applied to the length of the bar 12, V0. Forthis relation of V0 to V0, the junction 27 is biased in the reversedirection over its entire area because the region of P-typesemiconductive material 25 is negative relative to the voltage of thearea of the bar 12 directly beneath the junction 27. This reverse biasprevents hole current flow into the body of N-type semiconductor, andspace charge collects along side of the junction barrier. The entirearea of the junc tion 27 thus is biased in the reverse direction. Thiscondition is illustrated by the graph of Fig. 7 in which the relationbetween voltage and distance along the bar 12 is shown as being linear.

In the circuit shown in Fig. 5, the value of the voltage derived frombattery 35 is approximately equal to one-half the magnitude of thevoltage of battery 21. When this voltage relationship exists, thepotential of the P-type semiconductive region 25 is intermediate thevalues of the potentials of the N-type semiconductive region adjacentit. Thus, because of the potential gradient existing in the bar 12, thevalue of the voltage at the left side of the P-type region 25 is greaterthan the voltage of an N-type semiconductive region 37 adjacent it. Inthis area 37, therefore, the N-type region is negative with respect tothe P-type region 25 and the left side of the junction 27 acts as anemitter, i. e. is biased in the forward direction. This is indicated inFig. 5, by the lack of accumulated space charge in the area 37 of thejunction 27.

However, the voltage V0 applied to the dot 23 is less than the voltageexisting in a N-type region 39 adjacent the right side of the P-typesemiconductive region 25. Since the voltage V0 is less than thepotential existing in the N-type region 39 of the bar 12, the junctionof the N-type region 39 and the P-type region 25 is biased in thereverse direction, i. e. as a collector.

Therefore, when the value of the voltage Vc applied to the dot 23 isintermediate the value of voltage existing in the bar 12 at the sides ofthe region 25, the N-type region 37 and the P-type region 25 form anemitter junction and the N-type region 39 and the P-type region 25 forma collector junction. When this condition exists, the relation betweencurrent Ic flowing through the junction 27 and the voltage V0, appliedbetween the dot 23 and the contact 13, exhibits non-linear propertiesincluding a negative resistance region. Fig. 9 shows a graph of thiscurrent-voltage relation. The region AC of the voltage-current curve isthe negative resistance region. Because of this negative resistanceregion, a small increase in voltage from a value of C to a value of C+ACcauses a current increase from the value C to the current value at pointB. Thus, the device 11 is extremely sensitive to a small change involtage and is adapted to relay operation.

Fig. 10 shows a relay circuit utilizing the semiconductor device 11. Asin Fig. l, the battery 21 establishes a unidirectional potential acrossthe bar 12. The magnitude Vc, the potential of battery 29, is set at avalue slightly less than C (Fig. 9), and a coil 41 of a marginal relay43 is connected in series with the battery 29. The marginal relay 43 isadjusted so that it is insensitive to the normal flow of current throughthe coil 41. A source of controlling voltage 45 is connected toterminals 47 and 49 in series with the battery 29 so that the voltagesare additive.

When a controlling voltage pulse V is applied to the terminals 47- and49 from the source 45, the pulse voltage adds to the voltage Vc andbecause of the negative resistance region AC (Fig. 9) a rapid increaseof currents occurs, the magnitude of current changing from the value atpoint C to the value at point B. This electrical contact betweenterminals 51 and 52. As a result of the shorting of terminals 51 and 52,current from a source of potential 55 flows, through a device to becontrolled 57 thereby energizing it. If desired, the normally openmarginal relay .3. can be replaced by a normally closed relay, the onlydifference being that contact is broken instead of made when the currentflowing through coil 41 increases.

Fig. 11 illustrates a modification of the circuit shown in Fig. 10. Inthis modification the controlling voltage pulse Vp from source 45 isapplied to terminals 5-9 and 61, the polarity of Vp being as shown andis such as to subtract from the voltage V0 of battery 21. When acontrolling pulse is impressed between terminals 59 and 61, the voltagebetween contacts 13 and of the device 11 is decreased. This decrease involtage lowers the value of the unidirectional field in device 11 to apoint where the voltage Va is intermediate the values of axial voltageat the sides of dot 23. As previously explained this .condition resultsin a negative resistance characteristic for the current flowing throughthe dot 23. Therefore, the current increases from a value near point C(Fig. 9) to a value near point B and thus operates marginal relay 43 asexplained in the discussion of Fig. 10. Because the curve of Fig. 9 isdrawn for a particular value of V0, the exact currents flowing throughthe device it will not be equal to the values at point C or B. The curvewill be displaced slightly because the value of the voltage appliedbetween contacts 13 and 15 is changed by the amount of the controllingvoltage V The negative resistance region AC (Fig. 9) indicates that, asthe current increases, the voltage decreases. A physical explanation ofthis negative resistance region lies in the fact that, when minoritycarriers are injected into a semiconductive material having majoritycarriers, the resistance of the semiconductive material may beappreciably lowered. This is especially true of high resistivitysemiconductive materials. Since V=RI if I increases, the voltage willdecrease only if the percentage decrease in R is greater than thepercentage increase in I.

When any part of junction 27 becomes biased in forward direction, holesare emitted from the P-type region 25 into the l-type region. Theseinjected holes appreciably lower the resistance of the bar 12,especially in the region between the dot 23 and the ohmic contact 13. Toobtain the negative resistance region AC it is necessary that thequantity of semiconductive material into which the holes are injected besmall. Otherwise the holes injected into the bar 12 do not lower theresistance to the required degree because there are only relatively fewholes to change the resistance of a large quantity of semiconductivematerial. If, however, the total amount of semiconductive material issmall, the holes injected into the material cause a change in resistanceof the semi-conductive bar 12 between the dot 23 and ohmic contact 17that is appreciable with respect to the original resistance of thisregion of the bar 12, and thus as the number of holes injected into thebar 12 increase, that is, the current increases, the resistance of thebar 12 decreases by a larger percentage, thus creating the negativeresistance region A-C.

In an operative embodiment of this device the value of V0 isapproximately 22 /2 volts, and the dimensions of the bar 12 areapproximately .2 inch long by .1 inch wide by .01 inch thick.

The range of values of Va relative to V0 that gives the negativeresistance region A-C of the voltage current curve is herein describedas being distributed around a voltage approximately equal to one-halfthe value of V0. However, if the dot 23 is placed other than at themidpoint of the bar 12, the same results are obtained ut with diii rentr l i m g itudes of Va and V0. Such a figura i n i within he contemplaion of the present invention.

l ho gh y in nt n. ha be n des rib above in nne ion with pec fi em d m ns, many mod fications may be made. It is to be understood that I intendby the appended claims to cover all such modifications as fall withinthe true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the U. S.is:

l. A semiconductor device comprising a body of semiconuctive materialhaving conduction car e of o type predominating, a region of said bodyhaving conduction carriers of the other type predominating and with nsai b dy, a e tr e n- 7 and spaced from said junction, means electricfield in said means for establishing a pois intermediate the, potentialsaway from said electrode, tential at said region which junction and theone of said electrodes toward which injected carriers move beingsufficiently small that the resistivity thereof is appreciably changedby injection of greater than said predetermined value which variesdirectly with current flow.

between said electrodes, means for establishing a poten- 4 Incombination, a body of semiconductive material having conductioncarriers of one conductivity type predominating and having a pair ofspaced electrodes thereon, a load circuit, means for applying apotential between said electrodes through said load circuit, and meansfor controlling the current in said load circuit by minority carrierinjection comprising an input circuit connected between one of said twoelectrodes and the region of injection, said region of injection beinglocated on said body between said electrodes and having conductioncarriers of the opposite type predominating, said region being biased ata potential intermediate the potentials at said electrodes.

5. In combination, a body of semiconductive material having conductioncarriers of one conductivity type predominating and having a pair ofspaced electrodes thereon, means for applying a potential between saidelectrodes, means for controlling the current flow between saidelectrodes by minority carrier injection comprising a region havingconduction carriers of opposite type predominating, said region beingspaced on said body between said electrodes and being biased at apotential lying between the potentials at said electrodes.

6. In combination, a semiconducting body having a pair of baseelectrodes embracing a region of uniform conductivity type, means forapplying an electric potential between said base electrodes, anadditional electrode making rectifier contact with said body at a regionwithin the electric gradient produced by a diflerence in potentialbetween said base electrodes, and an electric circuit connected betweensaid additional electrode and one of said base electrodes and havingimpedance elements causing the potential of said additional electrode tolie within the potential range spanned by said base electrodes.

7. In combination, a semiconducting body of uniform conductivity typehaving a pair of base electrodes spaced at opposite ends of said body,means for applying an electric potential between said base electrodes,an additional electrode making a rectifier contact with said body, andmeans biasing said additional electrode to potentials within the rangespanned by said base electrodes.

8. A semiconductor device comprising a body of semi conductive materialof one conductivity type having a pair of spaced contacts thereon, aregion of another conductivity type in said body intermediate saidcontacts and forming a junction within said body, means for applying apotential between said contacts, means for applying a potential to saidregion which is intermediate the potential at said contacts, thedistance between said junction and that one of said ohmic contactstoward which injected carriers are attracted being sufliciently smallthat the resistivity of that portion of said body of one typeconductivity included therebetween is changed appreciably by injectiontherein of minority carriers from said region, the change in voltagebetween said region and said one contact varying inversely with thechange in current flow therebetween.

9. A semiconductor device comprising a bar of semiconductive material ofone conductivity type having first and second ohmic contacts at oppositeends thereof, and a region of opposite conductivity type intermediatesaid ohmic contacts forming a P-N junction with said bar, means forapplying a potential between said ohmic contacts, means for applying apotential to said region with respect to one of said contacts which isintermediate the potentials at the ends of said bar.

References Cited in the tile of this patent UNITED STATES PATENTS

